Task 8 - Reduced Energy Use through Reduced Indoor Contamination in Residential Buildings

The Task 8 has been completed. A copy of the final report NCEMBT is available for download in our Section "Downloads".

EXECUTIVE SUMMARY
According to the Freedonia Group, the consumer market for air cleaners, ranging from portable (room) to duct mounted (whole house) devices, grew 34% over a 5-year period to reach $395 million in 2004, and is estimated to reach $515 million by 2008. Homeowners, however, have only limited information available regarding their performance, especially for the combined removal of volatile organic compounds (VOCs) and particulates. A standard method of test for the removal efficiency of air cleaning devices under such conditions is lacking as well.

In this project, six “off the shelf” portable and two in-duct devices have been evaluated. Results are reported for their initial effectiveness to remove particulates and VOCs concurrently. All the tests were performed in a stainless steel environmental chamber. The devices were tested using a “pull-down” test procedure with simultaneous injection of potassium chloride particles ranging in diameter from 0.10 to 11m and a mixture of eight representative VOCs. Other important parameters, including ozone emission, power consumption, noise level and pressure drop (across in-duct devices), were also measured.
The tested products utilize different technologies for gas and particulate removal including sorption, media filtration, ultraviolet-photocatalytic oxidation (UV-PCO), electronic precipitation and air ionization. The potential effectiveness and energy benefit of using such devices to clean recirculated air to decrease the outdoor air intake and reduce the ventilation-related energy costs are briefly discussed and compared. Some considerations are also provided for engineering improvements of the air cleaners along with further research needs, including methods for extrapolating the chamber results to real homes.

The major findings from the testing and follow-up analysis are:
Media filtration and electronic precipitation are two effective methods to remove indoor particulate contaminants. The single portable electronic air cleaner tested had better performance (Clean Air Delivery Rate (CADR), removal efficiency and cost) than other portable air cleaners claiming the use of HEPA filters, but generated significant amounts of ozone. None of the four portable air cleaners claiming the use of HEPA filters approached a removal efficiency of ≥ 99.97%. The measured efficiencies ranged from around 50% to 80%. Further investigation revealed that the frames allowed some air to by-pass the HEPA filters. The tested ionizer unit, which features no fan and thus is quiet, only had very modest removal capacity for particulates while generating very significant amounts of ozone.
Sorption and UV-photocatalytic oxidation are two effective methods to remove indoor VOC contaminants, although most of off-the-shelf products are based on sorption technology. Only one UV-PCO in-duct air cleaner was tested and its performance, in terms of initial removal efficiency and cost, could not compete with an in-duct air cleaner with approximately 12 pounds of sorbent media. The tested ionizer unit without fan had no significant removal effect for all the tested VOCs. The removal efficiency for a specific VOC is related to its properties. For sorption technology, a heavier and low-volatility compound is generally expected to have a higher absorbability on activated carbon than a lighter and more volatile compound. For UV-PCO technology, the removal efficiency was found to be more closely related to the functional group of the chemicals.

The proposed test method worked well for portable air cleaners with nominal airflows of typically less than 400 cubic feet per minute (CFM). For in-duct air cleaners tested under rated operating airflow rates from 600 to 2000 CFM, accurate determination of CADR was difficult. A smaller recirculation flow rate (< 400 CFM) might improve the resolution of the test method if a reliable model were available to extrapolate the performance measured at a low airflow rate to high airflow rate(s). No significant difference was observed for particulate removal between tests with particle injection only and with simultaneous injection of particles and VOCs.

An analysis was performed to compare the energy cost between ventilation and use of a portable air cleaner using the simple steady-state model. Two cities, Syracuse, NY and Chicago, IL, were selected for analysis. Results indicate that there are significant savings using the best available air cleaner to replace the mechanical ventilation if particulates, toluene (or VOCs with vapor pressure smaller than 150 mmHg) or formaldehyde were the target pollutants. However, even the best portable air cleaner tested costs more than mechanical ventilation to provide the same clean air exchange rate for dichloromethane due to the low removal efficiency. In general, an air cleaner would need to perform better than $1.2/CADR (in Syracuse) or $3.75/CADR (in Chicago) for a target pollutant to obtain the energy cost benefit compared with mechanical ventilation.
 

This project was executed by Syracuse University under a subcontract to the Energy Resources Center (ERC) at the University of Illinois at Chicago (UIC) and (PSU).  The Principal Investigator is  Jianshun S. Zhang.

This project is complete.